1. Field of the Invention
This invention relates to the minimizing of the success of vehicle theft by employing a system which provides for safety locking up the vehicle brake hydraulic fluid in a manner to prevent movement of the vehicle and to provide a method for tying into existing auto theft alarms, should destructive tampering with the anti-theft system take place.
2. Description of the Prior Art
Vehicle anti-theft devices that perform a lock-up function of the hydraulic fluid in the wheel cylinders are exemplified by U.S. Pat. Nos. 3,515,442; 3,557,584; 3,559,755; 4,081,314; 4,040,675; 4,196,939. Each of these, by examination, offers a means of locking up hydraulic fluid to the wheel cylinders which activate the vehicle rakes. In each of these concepts, one-way check flow valves are utilized in one way or another to pass fluid from the master cylinder into the brake lines and wheel cylinders. None of the aove systems provides for the necessary accommodation of both heating and cooling effects caused by environment changes which expand and contract the hydraulic fluid. U.S. Pat. Nos. 4,018,314 and 4,040,675 have means, via check valves, to allow for thermal expansion relief but not for thermal contraction.
The ability to withstand thermal expansion and cooling contraction is very important, in that from a temperature of 40.degree. F. to 120.degree. F. a typical hydraulic fluid will undergo a density change of approximately 7% to 8%. This change with a system locked up provides for a major pressure change in the wheel cylinder, and results in the need for venting high-pressure buildup in the event of temperature increase; on the other hand, the pressure will rapidly fall off with a temperature decrease, and a one-way check system will not allow for both effects. Indeed, in some parts of the world, wide temperature changes on the order of 30.degree. F. to 60.degree. F. in one day can be expected to occur. A vehicle locked up at 60.degree. F. would not be so locked up at 0.degree. F.
U.S. Pat. No. 3,559,755 utilizes an electrical-operated solenoid control member for lock-up of the hydraulic fluid; whereas, the others referred to above are all manually operated to overcome possible loss of power effects. U.S. Pat. Nos. 4,018,314 and 4,040,675 place the aforementioned check valves integral with a primary operating valve function, and both patents provide for a mechanical lock position of the primary operating valve member; U.S. Pat. No. 4,018,314 utilizes a locking projection, operated by a key, to position the primary operating valve member; U.S. Pat. No. 4,040,675 utilizes a rotary cam action lock-up in conjunction with a key-operated cable. In both of these latter patents, the lock-up pressure is relieved by reposition of the primary operating valve member to release fluid towards the master cylinder. U.S. Pat. No. 4,196,939 and U.S. Pat. No. 3,557,584 accomplish the lock-up shut-off function by use of rotary mechanical motion to position and close shut-off parts.
Check valves as used in most of these patents, particularly multiple check valves, may also be subject to wear and tear by degradation by normal road- and engine-induced vibration, if no isolation from vibration effects is used; as a result, it is highly desirable to eliminate check valves if possible, or reduce their number to as few as possible, preferably one or none. The positioning of the primary valve member is important to error-free operation. Cam and lock-up positioning requirements result in added care in fabrication and assembly steps. Errors induced by such fabrication and assembly steps can be eliminated by use of symmetrical geometries that function regardless of position in assembly, and which are easily quality-checked in fabrication.
In order for any of these systems to function, the check valves must always be leak-tight and cannot allow the braking pressure to degrade rapidly with passage of time or usage. The slightest back leakage of hydraulic fluid over a small time will release the brake lock-up function. Further, under brake fluid hydraulic pressure load, the manual operation of the primary valving member by normal key arming movement will be very difficult, due to the effects of cumulated seal loads. Further, none of the above concepts provide for alarm safing at the arming mechanism to prevent tampering from immobilizing the entire anti-theft system.
The present invention disclosed herein is generally related to providing a means to deter theft of vehicles equipped with hydraulic fluid braking systems, while also providing safety interlocks into existing ignition systems and further means of adapting into audible alarm systems that presently exist for purposes of minimizing vehicle theft. The "SAFE LOCK ANTI-THEFT HYDRAULIC BRAKE CONTROL SYSTEM" comprises a compact control member which is readily adapted to existing braking systems through insertion of this compact control member into the hydraulic system between the master cylinder and the wheel cylinders, an interlock switch system which prevents auto ignition when the control member is activated, an accumulator system which accommodates temperature effects, and an arming system which sets the control member to lock the brakes of the vehicle. The accumulator system member automatically compensates for environmental thermal changes. No control passages or members are subject to normal-use vibration degradation. The control member is manually armed and requires no external electrical energy to operate.
The compact control member contains two separate piston assemblies which, by position, control brake hydraulic fluid flow in and out of the vehicle braking system through a series of ports. The larger piston assembly provides the actual control of fluid flow through selected ports, while the smaller activation piston assembly actually provides the arming and de-arming of the "SAFE LOCK ANTI-THEFT HYDRAULIC BRAKE CONTROL SYSTEM." The small activation piston assembly, in effect, allows for the necessary mechanical advantage effect to take place to automatically drive the larger piston assembly into the actual lock-up mode for the overall system. The control member, when inserted into the brake control of the vehicle, does not affect the normal front and rear brake functions.
Interconnected with the control member on the brake cylinder outlet sides of the control member is a small accumulator system. This accumulator system is designed such that it is only activated when the lock-up feature of the control member is activated. The accumulator system perfectly compensates for the effects of environmental temperature changes on the small braking system hydraulic fluid volume changes by either absorbing positive volume change or by feeding out fluid to accommodate negative volume change.
Connected to the small activation piston assembly of the control member is an arming system. This arming system further comprises an electrically isolated cable connected to an arming switch driven by a key, an electrically insulated metallic sheath electrically connected to other alarm systems on the vehicle. The key, driven manually through the cable connection, positions the small piston assembly in the control member for arming and de-arming the entire system.
Connected to the control member and activated by motion of the large piston assembly is an interlock switch. When the lock-up function is activated, this switch provides a means to prevent ignition from occurring. When the overall system is de-armed, the normal ignition function can occur.
To anyone familiar with the art, it can be seen that the invention disclosed herein eliminates the deficiencies of the above designs and offers a rugged, flexible and practical solution to the use of hydraulic lock-up means to minimize vehicle theft.